1. Field of the Invention
The present invention relates to a sliding material suitable for a sliding member of a bearing assembly, a method of manufacturing the sliding material, and the bearing assembly.
2. Related Art
Recently, with the progress of the industrial technology, it has been required to realize speed-up and high bearing stress of various bearings. Hitherto, as a sliding material for a sliding member of a bearing assembly, soft metallic materials, such as a white metal (first kind: Sn: 88 to 92 wt %, Sb: 5 to 7 wt %, Cu 3 to 5 Wt %, for example) have been used. However, melting point of these soft metallic materials is low so that the range of use is limited due to problems such as large reduction in strength and seizure at high temperature.
On the other hand, a polytetrafluoroethylene (PTFE) resin material has a low frictional coefficient and is excellent in heat resistance and hence is suitable for a sliding material of the bearing assembly. Further, a polyetheretherketone (PEEK) resin material and a polyimide (PI) resin material are excellent in mechanical properties at high temperature though they have a rather higher frictional coefficient in comparison with the PTFE resin material. To these resin materials, various ceramic fibers or particle fillers may be added so as to produce a sliding material combining mechanical properties with frictional and wearing characteristics.
For a bearing, especially for a bearing supporting a high load, it is required that a sliding member of a bearing is composed by using a sliding material produced by joining the above-mentioned resin material for a sliding plane member and a metallic base material for supporting the high load.
However, at the time of the joining between a resin material and a metallic material, in a conventional bonding method applied to the joining between metallic materials, it is difficult to have a sufficient bonding strength, providing a problem. For example, when different metallic materials are joined together by a molten metal solidification technique, a diffusion reaction occurs because of both metals are joined such that physical or chemical bonding occurs as well as mechanical bonding to achieve a sufficient bonding strength.
On the other hand, when a resin material and a metallic material are joined together by the molten metal solidification technique, it is difficult to have a sufficient bonding strength because of the simple mechanical bonding. When a resin material and a metallic material are joined together under high-temperature and high-pressure conditions, there may also cause a problem such that the resin material is deteriorated and the manufacturing cost increases due to long term duration under such conditions.
Furthermore, when a resin material and a metallic material are joined together, an adhesive may also be used. However, in this case, it is difficult to select an adhesive preferable for both the resin material and the metallic material. Furthermore, in a resin adhesive, since a junction interface certainly exists between the resin and the metal, the bonding strength between the resin material and the metallic material may not be essentially improved.
As a method for improving the strength of the junction interface between two kinds of members are joined, it has been known to increase a junction area by expanding a surface area with honing or chemical etching. However, since the expansion of the surface area with the honing or chemical etching has a limit and the resistance against the shear peeling off the junction interface is small, the bonding strength between different materials may not be improved sufficiently.
On the other hand, as a method of sufficiently improving the bonding strength between the resin material and the metallic material, it has been proposed to laminate resin materials on a surface of the metallic material while filling a resin material into a porous intermediate layer provided on the surface of a metallic material (refer to Patent Publication 1: Japanese Unexamined Patent Application Publication No. H10-29256).
According to the technique described in the above Patent Publication 1, it is necessary for the porous intermediate layer to be previously joined to the metallic material in vacuum condition. When composing a bearing for supporting a high load, such as a bearing for a hydraulic power generation instrument by using this technique, the sliding material of the bearing is composed of the sliding plane resin material and the metallic base material. In a case where the total weight of the sliding member of this bearing ranges from several hundreds kg to several tons, the process of joining the porous intermediate layer to the metallic base material will be performed in very large scale, so that the manufacturing cost is increased and there is a limit for vacuum equipment capacity.
In view of the above matters, when the sliding member of the bearing is produced by using a sliding material made by joining different materials, i.e., a resin material and a metallic material, it has been required to provide a preferable friction and wearing characteristics, an excellent sliding performance, and a desirable bonding strength between the sliding plane member and the base member, and not to depend on the equipment capacity, with reduced manufacturing cost.